1. Field of the Invention
This invention relates to packing optically coupled integrated circuits, and more particularly to optically coupled integrated circuits using flip-chip packaging methodologies.
2. Prior Art
Most electronic opto-couplers use discrete LEDs and silicon detectors. The LED is typically made from GaAs and the detector chip from silicon. The detector chip can either be a single discrete device such as a PN junction diode or a bipolar transistor or a detector device with additional support circuits such as amplifiers, buffers, etc. Also, the LED may require external buffers or driver circuits which are typically made from silicon. Because of the need to both electrically isolate each group of said devices and the different materials of the various components such as GaAs and silicon, hybrid techniques are used to fabricate these isolation devices. An added complication to the packaging of electrically isolated devices is the need to optically couple these devices.
In one packaging approach described in U.S. Pat. No. 5,049,527 the detector and its associated circuitry if present are placed on one portion of a lead frame and the GaAs LED and its associated circuitry if present are placed on another portion of the lead frame. One portion of the lead frame is then bent 180° so that the LED and detector are facing each other.
In another approach shown in U.S. Pat. No. 4,755,474 a transparent dielectric layer is placed on the silicon detector. A GaAs LED is then placed on top of the dielectric layer. This packaging concept is shown for a single discrete silicon detector and a single discrete LED. Hybrid techniques have also been used for coupling light communication signals from LEDs or from light detectors to fiber optic cables such as that discussed in U.S. Pat. Nos. 4,904,036 and 4,186,994.
In U.S. Pat. No. 5,199,087 fiberoptic filaments are used to connect either LEDs or light detectors to wave guides for the purpose of making external connections. The methods used to connect the filament to the chip surface include fusing pressure and strength with epoxy glue.
Using light detectors in conjunction with high gain amplifiers, it is possible to use low efficiency silicon based LEDs, as well as more efficient GaAs LEDs which can be deposited on silicon, to realize signaling circuits which require electrical isolation. Silicon based LEDs include forward biased PN junction diodes, avalanche PN junction diodes, porous silicon diodes, and deposited silicon carbide diodes. For example, using two silicon integrated circuits with “on chip” LEDs it is possible to build a telephone line interface circuit referred to as Data Access Arrangement (DAA), to build computer communications ports requiring isolation such as RS232, to build byte wide or larger bi-directional isolated digital ports, or to build optically isolated analog voltage sources.
The aforementioned patents do not address methods of packaging opto couplers in which LEDs are integrated onto silicon chips as well as light detectors. Also, these patents do not address the case in which there are multiple optical links between two silicon chips.